A method of generating a modulated signal using a modulated signal generating device that has a plurality of amplifiers aligned in parallel is known as a method of transmitting a modulated signal generated by superimposing a data signal on a carrier signal, such as medium-frequency broadcasting. The modulated signal generating device generates a modulated signal by performing on-off control on the amplifiers according to the frequency of the carrier signal and combining outputs from the respective amplifiers. The modulated signal generating device performs on-off control on the number of amplifiers corresponding to an amplitude value of the data signal, thereby obtaining a modulated signal having undergone amplitude modulation.
The above-described modulated signal generating device, however, performs on-off control on the amplifiers according to the frequency of the carrier signal, and the signal waveform of the modulated signal thus forms a rectangular waveform having the same frequency as that of the carrier signal. When a modulated signal is transmitted in a rectangular waveform, a band-pass filter is needed in order to remove unnecessary harmonic components from the modulated signal.